The proposed project is directed toward the following overall goals: 1) Purification and characterization of folate metabolizing enzymes such as dTMP synthetase, dihydrofolate reductase, 5,10-CH2 FH4 dehydrogenase and folyl-polyglutamate synthetase derived from human cells. 2) Study of the interaction of various folate metabolizing enzymes and their action with various forms of folyl-polyglutamates. 3) Designing and development of specific inhibitors for some folate metabolizing enzymes. 4) Study of the effects of these inhibitors on human cells in culture. 5) Study of the folate metabolism and folyl-polyglutamate synthesis in human cells. 6) Purification and characterization of folate binder derived from the membrane fraction of human cells. 7) Elucidation of the biological role of folate binder in human cells.